“Theories include vehicle fumes causing a photochemical smog that blocks pollen grains escaping into the upper atmosphere,” says Dr Carson, who is a member of the British Society for Allergy & Clinical Immunology.

“It may even make the pollen ‘stickier’ so that it enters – and stubbornly stays stuck – to vulnerable body organs (eyes, nose, sinuses, lungs).”

Dr Carson and his son have developed an app called HayFeverRelief that allows users to monitor pollen levels in their area and receive personalised advice on managing their allergies.

The app is available to download for free from the Apple App Store and Google Play.

What is hay fever?

Hay fever is an allergic reaction to pollen. While most people are affected by grass pollen, pollen from trees and flowers can also be a problem for some.

Symptoms can include a runny nose, watery eyes, sinus pain, sneezing, coughing and headaches. It affects 20 per cent of the population, including 80 per cent of people with asthma.

Pharmacists are urging people with hay fever to take preventative steps in order to minimise their symptoms ahead of peak hay fever season – June and July.

A word of warning though: as hay fever sufferers stock up on over-the-counter medicine, research reveals we need to be wary of getting behind the wheel when taking antihistamines.

Professor Ashok Soni, from the Royal Pharmaceutical Society, says: “There will be a warning on the packaging of medicine advising people not to drive or operate machinery if the medicine causes drowsiness.

“This isn’t always the case but it is best to avoid taking these if driving is essential.

“Even with medicines that don’t commonly cause drowsiness there is a small risk, so I would always advise people to see how they react to a medicine if taking it for the first time and not to drive unless they are sure they are okay.”

However, there are ways to treat hay fever that can allow you to drive safely and within the law.

Soni explains: “Depending on symptoms there are topical products available, nasal sprays and eye drops which won’t cause these symptoms so these are much better to use if driving is essential.

“If you must drive then use eye drops and nasal sprays in preference. Always keep windows closed and even when parked don’t leave windows or doors open as pollen can be trapped in the car.”